The present invention relates to zinc-modified phenolaldehyde novolak resins, and more particularly, to an improved method for making zinc-modified phenol-aldehyde novolak resins which are particularly useful in carbonless copy paper manifold systems as color-developing agents (coreactants) for colorless chromogenic materials.
The carbonless manifold systems generally comprise a substantially colorless developing agent, a substantially colorless chromogenic material and a common solvent or solvent mixture for each. The color-developing agents in the chromogenic material are isolated from each other on the surface of a substrate such as paper. The solvent may be isolated from each of the other ingredients or may contain either ingredient, usually the chromogenic material, in solution. Preferably, the colorless chromogenic material and the solvent are encapsulated in microcapsules as disclosed in U.S. Pat. Nos. 2,800,457; 3,041,289; 3,533,958 and 4,001,140. The configuration and relationship of either reactive component in the solvent can be of any of those disclosed in U.S. Pat. No. 3,672,935. The microcapsules containing a solution of the colorless chromogenic material may be applied with an adhesive or binder to one surface of a substrate such as paper. The color-developing agent may be applied as a coating to a second substrate, either alone or mixed with other ingredients such as adhesives or binders and mineral particles. When the two substrates are superimposed one on the other with the coated surfaces in contact with each other and then subjected to pressure, the microcapsules are ruptured in the configuration of the applied pressure, and the solution of colorless chromogenic material is transferred in the same configuration to the surface of the substrate containing the coating of the colordeveloping agent to form a colored mark on the surface, again in the configuration of the applied pressure. The microcapsules and color-developing agent may also be applied to the same surface of a substrate such as paper either as a mixture or as separate coatings. Pressure applied to several of these sheets superimposed one on the other produces a mark in the pattern of the indicia of the applied pressure. Other configurations include microcapsules containing a solution of the color-developing agent in which case the colorless chromogenic material is applied as a second coating to the same or a different substrate.
Zinc-modified-phenol-aldehyde novolak resins and methods of producing such resins for use as a color-developing agent for basic colorless chromogenic materials are known. U.S. Pat. No. 3,732,120 discloses a method of making such zinc-modified phenol-aldehyde novolak resins wherein a zinc compound such as zinc dibenzoate is added to a para-substituted phenolaldehyde novolak resin. The resulting zinc-modified novolak resin is cooled, ground and then coated onto a paper substrate in one or more of the configurations previously described. Improved resistance to print fade and increased color intensity were obtained by the use of the zinc-modified resin product when compared to the novolak resin material alone as a color-developing agent for oil-soluble basic colorless chromogenic materials in carbonless copy paper manifold systems.
U.S. Pat. No. 3,737,410 discloses a method of making zinc-modified para-substituted phenol-formaldehyde novolak resins which comprises mixing together and heating a zinc compound such as zinc dibenzoate, a weak base such as ammonium bicarbonate and an unmodified phenol-aldehyde resin material. Again, the resulting zinc-modified novolak resin provides improved color intensity and fade resistance as well as increased print speed and improved resistance to coreactant-surface sensitivity.
U.S. Pat. No. 4,025,490 discloses a similar method of producing zinc-modified para-substituted phenol-formaldehyde novolak resins comprising melting together with mixing, a composition of a material such as zinc formate, ammonia or an ammonium compound such as ammonium carbonate, and a para-substituted phenol-aldehyde novolak resin. It is stated that the resulting zinc-modified resin material provides an improved rate of color image development, fade resistance, and storage stability in a carbonless copy paper manifolding system prior to imaging the coreactant surface. It is also disclosed that the inclusion of the weak ammonium compound (ammonium carbonate) or ammonia gas suppresses the formation of metal oxide during the melting process. The metal oxide formed during the melting in effect prevents that portion of the metal from entering into modification of the novolak resin.